This invention relates to esteramide copolymer resins for use as hot melt adhesives particularly for shoe manufacture and to adhesive processes based on the special properties of the adhesives.
In the attaching of outsoles to shoe uppers, presently preferred adhesives are of the solution type based on polyurethane or polychloroprene. These cements are applied on the attaching surfaces of both the outsole and the shoe upper, are dried to remove the solvent, and are then activated by heat before assembly. The polyurethane adhesive is particularly useful because it will adhere well to leather, polyvinylchloride, and polyurethane shoe upper materials. However, in use of each of these adhesives the matter of driving off of the solvent as well as disposing of solvent vapors inherent in drying the adhesives are objectionable.
It has also been proposed to attach outsoles to shoe uppers using hot melt adhesives applied in molten form to the shoe sole and pressed against the shoe upper while the adhesives are still molten. The process is critical in terms of careful timing to insure assembly before the adhesive hardens. Also the resins used for the adhesives i.e. copolyester resins, do not adhere well to urethane shoe upper material. Efforts to use polyester urethane resins as hot melt adhesives were not successful since the urethane linkage tended to decompose, producing carbon dioxide gas that disrupts pumping and feeding in machine application.